Semiconductor device

ABSTRACT

A semiconductor device includes: a first heat spreader; a second heat spreader separated from the first heat spreader; a first semiconductor element on the first heat spreader and having a back face jointed to the first heat spreader; a second semiconductor element on the second heat spreader and having a back face jointed to the second heat spreader; a resin coating the first and second heat spreaders and the first and second semiconductor elements; and a reinforcing member provided across a region between the first and second heat spreaders in the resin, and having rigidity higher than rigidity of the resin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device used in aninverter to control a motor used in automobiles or electric trains, orin a converter for electric generation or regeneration.

2. Background Art

A semiconductor device wherein a semiconductor element is mounted on aheat spreader, and the heat spreader and the semiconductor element aresealed with a resin has been used (for example, refer to Japanese PatentApplication Laid-Open No. 2004-165281).

SUMMARY OF THE INVENTION

In a semiconductor device wherein each of semiconductor elements ismounted on two heat spreaders separated from each other, a resin ispresent in the region between the two heat spreaders. Due to thedifference in the linear expansion coefficients between the resin andthe heat spreader, when heat is generated and temperature change occursduring the use, thermal stress occurs. For this reason, when excessivehot-cold cycles are applied, a warpage occurs from the region betweenthe two heat spreaders. Further, there has been a problem whereinabrasion develops between the resin and internal members such as theheat spreader or lead frames, and reliability is affected.

In view of the above-described problems, an object of the presentinvention is to provide a semiconductor device which can inhibit thewarpage by thermal stress and improve the reliability.

According to the present invention, a semiconductor device includes: afirst heat spreader; a second heat spreader separated from the firstheat spreader; a first semiconductor element on the first heat spreaderand having a back face jointed to the first heat spreader; a secondsemiconductor element on the second heat spreader and having a back facejointed to the second heat spreader; a resin coating the first andsecond heat spreaders and the first and second semiconductor elements;and a reinforcing member provided across a region between the first andsecond heat spreaders in the resin, and having rigidity higher thanrigidity of the resin.

The present invention makes it possible to inhibit the warpage bythermal stress and improve the reliability.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a semiconductor device according tothe first embodiment of the present invention.

FIG. 2 is a perspective top view showing the interior of thesemiconductor device according to the first embodiment of the presentinvention.

FIG. 3 is a perspective top view showing the interior of thesemiconductor device (from which reinforcing members are omitted)according to the first embodiment of the present invention.

FIG. 4 is a sectional view taken along the line I to II in FIG. 2.

FIG. 5 is a sectional view taken along the line III-IV in FIG. 3.

FIG. 6 is a perspective top view showing the interior of a semiconductordevice in a modification example (from which reinforcing members areomitted) according to the first embodiment of the present invention.

FIG. 7 is a sectional view showing a semiconductor device according tothe second embodiment of the present invention.

FIG. 8 is a perspective top view showing the interior of a semiconductordevice according to the third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A semiconductor device according to the embodiments of the presentinvention will be described with reference to the drawings. The samecomponents will be denoted by the same symbols, and the repeateddescription thereof may be omitted.

First Embodiment

FIG. 1 is a circuit diagram showing a semiconductor device according tothe first embodiment of the present invention. Six pairs of transistorelements 1 a to 1 f and diodes 2 a to 2 f constitute a three-phasehalf-bridge circuit. An electric power from a power source is suppliedto the load via U, V, and W terminals. The transistor elements 1 a to 1f are insulated gate bipolar transistors (IGBT) which conduct electriccurrents supplied from the power source for only required times. Thediodes 2 a to 2 f reflux electric current when the transistor elements 1a to 1 f become the blocking state from the conducting state.

FIG. 2 is a perspective top view showing the interior of thesemiconductor device according to the first embodiment of the presentinvention. FIG. 3 is a perspective top view showing the interior of thesemiconductor device (from which reinforcing members are omitted)according to the first embodiment of the present invention. FIG. 4 is asectional view taken along the line I to II in FIG. 2.

Heat spreaders 3 a to 3 c and heat spreaders 3 d to 3 f are separatelyarranged on the left and the right. The heat spreaders 3 a to 3 f areseparated from each other. The transistor elements 1 a to 1 c and thediodes 2 a to 2 c are respectively mounted on the heat spreaders 3 a to3 c, and the back faces thereof are separately joined to the heatspreaders 3 a to 3 c with a solder 4. The transistor elements 1 d to 1 fand the diodes 2 d to 2 f are respectively mounted on the heat spreaders3 d to ef, and the back faces thereof are separately joined to the heatspreaders 3 d to 3 f with the solder 4.

Wiring members 5 a to 5 c separated from each other are respectivelyjoined to the upper faces of the transistor elements 1 a to 1 c and thediodes 2 a to 2 c with the solder 4. A wiring member 5 d is joined onthe upper faces of the transistor elements 1 d to 1 f and the diodes 2 dto 2 f with the solder 4 in common. In place of the solder 4, aconductive adhesive or the like can also be used. The wiring members 5 ato 5 c are respectively joined to the peripheral portions on the upperfaces of the heat spreaders 3 d to 3 f. Wiring members 5 e to 5 gseparated from each other are respectively joined to the peripheralportions on the upper faces of the heat spreaders 3 a to 3 c.

Signal wirings 6 a to 6 c are respectively connected by wires to thecontrol terminals of the transistor elements 1 a to 1 c. Signal wirings6 d to 6 f are respectively connected by wires to the control terminalsof the transistor elements 1 d to 1 f. For insulation from the exterior,an insulating layer 7 is provided on the back face of the heat spreaders3 d to 3 f. These heat spreaders 3 a to 3 f, the transistor elements 1 ato 1 f, the diodes 2 a to 2 f, parts of the wiring members 5 a to 5 g,parts of the signal wirings 6 a to 6 f, and the upper faces and the sidefaces of the insulating layer 7 are coated with a molding resin 8.

The wiring members 5 a to 5 g assume receiving and sending the electricpower from and to the exterior of the device. The wiring members 5 a to5 g and the signal wirings 6 a to 6 f are formed in the state wherein,for example, the identical metal plates are punched or etched to beintegrally connected at the outer frame. Parts of them are coated withthe molding resin 8 to mechanically hold them, and the outer frame isremoved to divide the wiring members 5 a to 5 g and the signal wirings 6a to 6 f. Thereby, since a large number of wiring members 5 a to 5 g andsignal wirings 6 a to 6 f can be assembled at once, the productivity isimproved, and the industrial value is elevated.

In the present embodiment, a reinforcing member 9 having the rigidityhigher than the rigidity of the molding resin 8 is provided across theregion between heat spreaders 3 a to 3 f in the molding resin 8. Thereinforcing member 9 is provided above the transistor elements 1 a to 1f and the diodes 2 a to 2 f without contacting to the transistorelements 1 a to 1 f and the diodes 2 a to 2 f.

The reinforcing member 9 is, for example, a metallic plate member. Ifthe reinforcing member 9 is a metallic member, it has a sufficientlyhigher Young's modulus than the molding resin 8. Therefore, thereinforcing effect can be improved. In addition, when the reinforcingmember 9 is fabricated with organic materials reinforced likefiber-reinforced plastics, ceramic materials, or the like, it ispreferred for weight saving. Further, the reinforcing member 9 is notlimited to a plate shape, but can have an L- or U-shape so as to inhibitbending.

By reinforcing the region between the heat spreaders 3 a to 3 f with thereinforcing member 9, the warpage caused by thermal stress can beinhibited in such a region. As a result, breakage can be prevented andreliability can be improved.

In addition, the transistor elements 1 a to 1 f, the diodes 2 a to 2 f,the heat spreaders 3 a to 3 f, the wiring members 5 a to 5 g, and thesignal wirings 6 a to 6 f constitute a three-phase half bridge circuitrequired in the invertor circuit for controlling the load of the motoror the like. As described above, in the case where a three-phase halfbridge circuit is constituted with one semiconductor device, the packagesize is enlarged, and the problem of warpage becomes significant.However, since warpage can be inhibited by the constitution of thepresent embodiment, the reliability can be improved.

Further, the wiring members 5 a to 5 c intersect the region between theheat spreaders 3 a to 3 c and the heat spreaders 3 d to 3 f to connectthe upper faces of the transistor elements 1 a to 1 c and the heatspreaders 3 d to 3 f, respectively. With functioning as electriccircuits, the wiring members 5 a to 5 c can reinforce the relevantregion. Therefore, without increasing the number of parts, the warpageby thermal stress can be inhibited. As a result, the reliability can beimproved without impairing productivity.

FIG. 5 is a sectional view taken along the line III-IV in FIG. 3. Evenif the wiring members 5 a to 5 c have a flat structure, reinforcingeffects can be obtained due to the rigidity of the metal. However, byproviding a U-shaped indent 10 in parts of the wiring members 5 a to 5 cin the direction from the upper face to the back face, the rigidity inthe thickness direction can be improved. If the depth of the indent 10is about 1.5 times the thickness of the wiring members 5 a to 5 c,processing can be performed, and a sufficient reinforcing effect can beobtained. Further, the indent 10 can be provided in the direction fromthe back face to the upper face of the wiring members 5 a to 5 c. Theshape of the indent 10 is not required to be U-shaped, but can betriangular or semicircular.

FIG. 6 is a perspective top view showing the interior of a semiconductordevice in a modification example (from which reinforcing members areomitted) according to the first embodiment of the present invention. Thetransistor elements 1 a to 1 c and the diodes 2 a to 2 c are mounted onone heat spreader 3 g in parallel and the back faces thereof arecommonly joined to the heat spreader 3 a with the solder 4. Thereby, theleft side of the device is supported by the heat spreader 3 g having ahigh rigidity. A wiring member 5 h is joined to the peripheral portionof the upper face of the heat spreader 3 g.

As described above, the heat spreaders 3 a to 3 c having the samepotential are gathered to one heat spreader 3 g, and the warpage of thepackage in the longitudinal direction of the heat spreader 3 g can bereduced. In addition, the number of the parts can be reduced, and theassembly can be simplified. Furthermore, it is preferable that thelongitudinal direction of the heat spreader 3 g is parallel to theterminal takeout face of the package because wiring is easy. However,the vertical direction to the terminal takeout face is also feasible.

Second Embodiment

FIG. 7 is a sectional view showing a semiconductor device according tothe second embodiment of the present invention. Since insulation betweenelements is ensured under the insulating layer 7, a copper foil 11 isprovided under the insulating layer 7 across a plurality of heatspreaders 3 a to 3 f. The copper foil 11 is thicker than the insulatinglayer 7, and intersects the region between the heat spreaders 3 a to 3f. By reinforcing the region between the heat spreaders 3 a and 3 f withthe thickened copper foil 11, the warpage caused by thermal stress inthe region can be inhibited. As a result, breakage can be prevented andreliability can be improved. In addition, the copper foil 11 can also beused as the adhesion of the package and the cooler.

Third Embodiment

FIG. 8 is a perspective top view showing the interior of a semiconductordevice according to the third embodiment of the present invention. Theheat spreader 3 g has a concave portion 12 facing the heat spreaders 3 dto 3 f. The heat spreaders 3 d to 3 f have extended portion 13 enteringinto the concave portion 12. Thereby, the region between the heatspreader 3 g and the heat spreaders 3 d to 3 f are reinforced, andwarpage caused by thermal stress in the region can be inhibited. As aresult, breakage can be prevented, and reliability can be improved. Inaddition, although the shape of the extended portion 13 is preferablyrectangular along the shape of the semiconductor element, it can becurved like an S-line, or can be triangular.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

The entire disclosure of a Japanese Patent Application No. 2012-103244,filed on Apr. 27, 2012 including specification, claims, drawings andsummary, on which the Convention priority of the present application isbased, are incorporated herein by reference in its entirety.

What is claimed is:
 1. A semiconductor device comprising: a first heatspreader; a second heat spreader separated from the first heat spreader;a first semiconductor element on the first heat spreader and having aback face jointed to the first heat spreader; a second semiconductorelement on the second heat spreader and having a back face jointed tothe second heat spreader; a resin coating the first and second heatspreaders and the first and second semiconductor elements; and areinforcing member provided across a region between the first and secondheat spreaders in the resin, and having rigidity higher than rigidity ofthe resin.
 2. The semiconductor device according to claim 1, wherein thereinforcing member is provided above the first and second semiconductorelements without contacting to the first and second semiconductorelements.
 3. The semiconductor device according to claim 1, furthercomprising an insulating layer provided on back faces of the first andsecond heat spreaders, wherein the reinforcing member is a metal layerprovided under the insulating layer and thicker than the insulatinglayer.
 4. A semiconductor device comprising: a first heat spreader; asecond heat spreader separated from the first heat spreader; a firstsemiconductor element on the first heat spreader and having a back facejointed to the first heat spreader; a second semiconductor element onthe second heat spreader and having a back face jointed to the secondheat spreader; and a resin coating the first and second heat spreadersand the first and second semiconductor elements, wherein the first heatspreader has a concave portion facing the second heat spreader, and thesecond heat spreader has an extended portion entering into the concaveportion.
 5. The semiconductor device according to claim 1, furthercomprising a wiring member connecting an upper face of the firstsemiconductor element to the second heat spreader and having an indent.6. The semiconductor device according to claim 1, wherein the firstsemiconductor element includes a plurality of semiconductor elements,and back faces of the plurality of semiconductor elements are commonlyjoined to the first heat spreader.
 7. The semiconductor device accordingto claim 1, wherein the first and second heat spreaders and the firstand second semiconductor elements constitute a three-phase half-bridgecircuit.
 8. The semiconductor device according to claim 4, furthercomprising a wiring member connecting an upper face of the firstsemiconductor element to the second heat spreader and having an indent.9. The semiconductor device according to claim 4, wherein the firstsemiconductor element includes a plurality of semiconductor elements,and back faces of the plurality of semiconductor elements are commonlyjoined to the first heat spreader.
 10. The semiconductor deviceaccording to claim 4, wherein the first and second heat spreaders andthe first and second semiconductor elements constitute a three-phasehalf-bridge circuit.